Contemporary practice in the art typically uses a synchronizing signal alteration method for image positioning in an image processing apparatus. Positioning of a video signal being visually displayed on a variable visual monitor, such as a cathode ray tube, is altered by electrical operation of a synchronizing signal. The positioning of a raster is substantially shifted according to phases of both horizontal and vertical synchronizing signals in the directions of up, down, left and right, with respect to the frame angle of a display. Upon positioning adjustment of a video signal being visually displayed on a monitor by user manipulation, it is required to generate and utilize a pseudo-synchronizing signal whose phase has been shifted with respect to the phase of its inherent synchronizing signal. Generally, generation a pseudo-synchronizing signal having a different phase with respect to its inherent synchronizing signal, such as a horizontal or vertical synchronizing signal assumed to be applied from an external source, incorporates a pair of monostable multivibrators, respectfully synchronized with a rising edge of an input signal and with a failing edge of an input signal, thereby generating a pulse having a predetermined pulse width. Such pseudo-synchronizing signal such as a cathode ray tube. It is well known in the art regarding circuits for generating pseudo-synchronizing signals to be improper to adopt such pseudo-synchronizing signal generating circuits for use in a digital signal display apparatus, especially in a liquid crystal display. Upon applying a pseudo-synchronizing signal from a conventional circuit apparatus, an asynchronous phenomenon between a pseudo-synchronizing signal and a video dot clock signal occurs thereby causing a failure to the apparatus.
Shuji Ishihara describes a Timing Pulse Generator For Generating Timing Pulses Synchronized With The Horizontal Synchronizing Signal In A Video Signal in U.S. Pat. No. 4,736,162 for controlling the positioning of an image to be superimposed on a video image. Ishihura does not contemplate generating a second pseudo-synchronizing signal as a selected one of a first pseudo-synchronizing signal and a horizontal synchronizing signal in responsive to a program data signal.